1. Field of the Invention
This invention relates to a lubricating oil composition which reduces wear between relatively moving surfaces while providing protection, concomitantly from sludge formation and corrosion.
2. Description of the Prior Art
A balanced formulated lubricating oil for use in an internal combustion engine normally contains additives which will protect against wear, act as antioxidants, corrosion inhibitors and detergent-dispersants.
In the past many hydrocarbyl dithiophosphate compounds have been employed as additives in lubricant compositions primarily to reduce wear and to act as antioxidants. Of the many compounds employed, perhaps the best known are zinc salts of O,O'-dihydrocarbyl dithiophosphoric acids.
Also, since lubricating oils tend to deteriorate under conditions of use in the present day automobile engine, with the attendant formation of sludge, lacquer and resinous materials, it is common to add agents which are known in the art as detergents, dispersants or detergent-dispersants. Overbased metal hydrocarbyl sulfonates are particularly useful in this respect. These agents are believed to be effective because they provide alkalinity capable of neutralizing strong organic and inorganic acids and are capable of dispersing deposits and deposit precursors into the oil phase.
It has been found, however, that lubricating oils containing overbased calcium hydrocarbyl sulfonates tend to offset the effectiveness of the normal metal salts of dihydrocarbyl dithiophosphoric acids to provide sufficient wear protection in the internal combustion engine of an automobile. This is particularly true in high calcium ash formulations containing from about 1% to 2.5% by weight ash content. This is an especially bad situation at this time since automobile manufacturers are seeking to use lower levels of metal salts of dihydrocarbyl dithiophosphoric acids in lubricating oils in order to protect against deterioration in performance of the emissions control system--both catalyst poisoning and oxygen sensor contamination are involved.